In a conventional gear pump as illustrated in FIG. 6, a pair of gears 2 and 3 meshing with each other are rotatably contained in a gear case 1 which is closed by side plates 4 at both sides thereof.
As illustrated in FIG. 7, seals 5 are disposed between the case 1 and the side plates 4 for preventing oil leakage and for providing a pressure balancing high pressure chamber in the gear case 1.
Each of the seals 5 has a shape as illustrated in FIG. 8 and cross sectional shapes as illustrated in FIGS. 9(a), 9(b), 9(c) and 9(d) respectively. The seals comprise projections 5a made of rubber and projections 5b formed by injection molding of fluorocarbon resin.
In the conventional seal device for the gear pump, there is a possibility of generating a crack a at the connecting part 5c of projections 5a when a tensile force acts on the connecting part 5c shown in FIG. 9(d) if an inner pressure is applied to the seal 5.
No oil leakage occurs at the crack a in the connecting part 5c. However, if the crack a develops to thereby generate new cracks b at the projections 5a, there is a likelihood of oil leakage at the cracks b.
Accordingly, the present invention has been made to solve the drawbacks set forth above and to provide a seal device for a gear pump capable of generating cracks concentratedly at the connecting part of projections to thereby prevent oil leakage.